The present invention relates to a self-orientating twin castor of the type comprising a pair of coaxial wheels.
Such castors are fitted to chairs and pieces of furniture. In particular for fitting to chairs, castors are also known having a braking system which is activated when the user rises from the chair and therefore no longer bears with his weight on the castors.
The operation of the braking system complies with safety criteria and its purpose is to brake the movement of the chair away from its position of use when the user is about to sit on it.
From U.S. Pat. No. 4,290,166 by the same Applicant, a wheel braking device, is known, which relates to this type of castor, for example. In this device, a spring is inserted, from below, in a vertical seat of the part that constitutes the castor support, so that it can act, with its lower end, on a shaft which supports, at its opposite ends, the two wheels of the castor. When the chair is not being used, the shaft is raised in a position in which the wheels abut against elements of the support suitable to prevent their rotation. Although the introduction of this type of castor is to be considered as an important improvement in this particular sector, there are still functional problems suffered by these devices.
In castors of the self-orientating type there is the certainly known problem of the collection of dust, dirt in general and other hard-to-remove materials between the wheels and the rotation shaft on which said wheels are fitted. This rather frequent drawback inevitably causes a deterioration of the internal components of the castor and significantly increases friction between the rotating elements to the point of preventing the rotation of the wheels.
Another problem suffered by all castors with twin wheels is that the wheels, when loaded, tend to assume a diverging arrangement due to elastic deformation. The consequence of this deformation is that the braking elements fitted inside the castor tend to rub against other parts of the castor and particularly affect the internal ribs designed to retain said braking elements in their working seats.
Another problem of twin castors in general is due to the use of lubricant in order to allow smooth wheel rotation. Even if said lubricant is dense, it tends to flow out of the castor and therefore soil the floor or, worse still, carpets and moquette.
The aim of the present invention is therefore to provide a self-orientating castor with twin wheels produced by molding plastic material which is capable of maintaining durable and effective operation and in particular prevents accumulation of dust or debris inside it.
Within the scope of this aim, an object of the present invention is to provide a self-orientating castor having a more effective braking system than that achieved in conventional castors.
Another object is to provide a self-orientating castor which has a simple and sturdy structure, allows rapid assembly and does not require particularly complicated molds, so as to be economically advantageous to manufacture.
This aim and these and other objects which will become better apparent hereinafter are achieved by the present self-orientating twin castor of the type that comprises: a supporting body, having a substantially vertical wall; a slot, vertically elongated and passing through said wall; a shaft, driven through said slot; a pair of wheels associated with the opposite ends of said shaft; a vertical receptacle, which is provided in said wall and is axially offset with respect to said shaft; a pivot, being rotatable in said receptacle for connecting the castor to a piece of furniture; two tubular portions, which protrude from opposite sides of said vertical wall and are substantially coaxial to said shaft; a substantially vertical hole, which is provided in said wall above said slot and is connected thereto; a spring, accommodated in said hole and acting on said shaft; characterized in that said hole is open upward and is closed by a closure element which acts as abutment for said spring.